Ultra high efficiency ballast increases lumen output. Lateral cathode design optimizes thermal efficiency. Exclusive end of life circuitry. Long life, 12,000 hours average rated life. The design and construction improves lumen maintenance over the complete life of the bulb. Special Application Notes: Up to 23 watt is UL approved for totally enclosed fixtures. Use a 27w and 32w in an open recessed can Do not use a 27w and 32w in an enclosed recessed can. Use voids the warranty. Do not use a 42w in an enclosed or open recessed can or any type of enclosed fixture. Use voids the warranty. Do not use more than two lamps in any type of enclosed luminaire.